Proximal Humerus Fracture: Hemiarthroplasty



Proximal Humerus Fracture: Hemiarthroplasty


Evan M. Michaelson

Alexis Williams

Evan L. Flatow



INTRODUCTION

Proximal humerus fractures account for roughly 6% of all adult fractures and have an annual incidence of 6 per 10,000 people in the United States.1 Similar to other osteoporotic fractures, proximal humerus fractures demonstrate a bimodal distribution with a smaller peak in young patients experiencing high-energy trauma and a higher peak in older patients more commonly associated with lower-energy trauma and ground level falls.2 The incidence is approximately 25 per 10,000 people in the Medicare population, with trends showing increasing numbers of these fractures.3 Neer, unhappy with the results of head resection then popular for these fractures, and inspired by the work of the Judet brothers with an acrylic prosthesis for the hip, first described the use of primary arthroplasty for treatment of proximal humerus fractures in 1953. After reporting his results in 1970, hemiarthroplasty became the gold standard for treatment of four-part fracture-dislocations and intra-articular fractures.4 Despite the exponentially growing popularity of reverse shoulder arthroplasty (RSA), hemiarthroplasty is still indicated in specific circumstances, including younger higher-demand patients at high-risk for persistent symptoms, functional loss, or fixation failure after proximal humerus fracture. Hemiarthroplasty remains a fundamental technique in the shoulder surgeon’s armamentarium for the treatment of proximal humerus fractures.




INDICATIONS

While many proximal humerus fractures may be managed nonoperatively, others are more appropriately treated surgically. With technological advancements, including locking plate fixation,5 minimally invasive percutaneous techniques,6 and RSA,7 the indications for hemiarthroplasty have thinned. Customarily, osteosynthesis techniques are reserved for fracture patterns with a lower risk of humeral head ischemia (ie, head preserving). Fracture patterns with increased risk of humeral head ischemia have a higher rate of avascular necrosis, hardware failure, malunion, and, ultimately, posttraumatic arthritis, complications that are all associated with poorer outcomes.8 Patients presenting with proximal humerus fracture dislocations treated with osteosynthesis experience high rates of revision surgery, and patients who undergo revision arthroplasty after failed fracture fixation have inferior outcomes compared with those treated with primary arthroplasty after proximal humerus fracture.9 Similarly, patients with head-split fractures experience very high rates of complications after osteosynthesis.10 Therefore, classic four-part proximal humerus fracture dislocations and intra-articular, or head-splitting, fractures are indications for head-sacrificing techniques (ie, arthroplasty). The contrast between classic four-part fractures and valgus-impacted fractures should be noted. The classic four-part fracture dislocations lack the vascular supply and mechanical support of the medial calcar hinge that is seen in valgus-impacted fractures.11

In recent practice, RSA has surpassed hemiarthroplasty in the treatment of complex proximal humerus fractures because the majority of these fractures are seen in elderly patients. These older, lower-demand patients have comorbidities such as osteoporosis and rotator cuff deficiency that make RSA a more reliable treatment option. RSA provides a lower risk of functional deficit and treatment
failure when compared with hemiarthroplasty for these patients, as it is less reliant on tuberosity healing.12 Hemiarthroplasty is reserved for classic four-part fracture dislocations or head-splitting fractures in younger or higher-demand patients with good bone quality. Hemiarthroplasty has the potential to provide improved range of motion and avoidance of the complications associated with glenoid replacement, such as loosening or notching.13 Finally, hemiarthroplasty is an option for patients with complex proximal humerus fractures in the setting of concomitant glenoid fracture precluding glenoid fixation and RSA.




CONTRAINDICATIONS

Contraindications to hemiarthroplasty for proximal humerus fracture relate to the expectation of improved outcomes with other treatment options. Simple fracture patterns and fractures with minimal displacement are indicated for nonoperative management. Operative fixation techniques such as open reduction and internal fixation or percutaneous pinning should be attempted in younger, active patients with reasonable bone quality and fracture patterns amenable to head-preserving techniques. Elderly patients with osteoporosis, comminuted tuberosity fractures, or concerns regarding rotator cuff integrity are at high risk for tuberosity healing complications or rotator cuff failure and are therefore better treated with RSA. Proximal humerus fracture nonunion with retracted tuberosities is a relative contraindication to hemiarthroplasty, as it is difficult to achieve tuberosity healing to the prosthesis and adequate rotator cuff function in this scenario.14 Active shoulder infection, significant glenoid arthritis, and severe medical comorbidities precluding surgical intervention are also contraindications to hemiarthroplasty.


PREOPERATIVE PREPARATION

Preoperative management focuses on identifying the appropriate patient for hemiarthroplasty. The mechanism of injury should be identified with specific focus on high- compared with low-energy trauma. Chronicity of fracture-associated injuries and ipsilateral fractures should be identified. Medical history should be documented including comorbidities, along with alcohol, tobacco, and drug use. Prior shoulder function should be assessed, including any prior surgery or injury to the ipsilateral shoulder, shoulder pain prior to injury, and rotator cuff function. The physical demands of the patient including work and recreation habits should be assessed, along with the use of any upper extremity-reliant assistive devices for ambulation and activities of daily living.

The physical examination is often limited in the setting of proximal humerus fracture. The shoulder should be inspected for loss of expected contour, ecchymosis, abrasion, swelling, and any possible open laceration. The surrounding structures including the acromioclavicular joint, scapula, and elbow should be palpated to assess for injury. Many patients will not tolerate passive or active range of motion. Ideally, the deltoid and rotator cuff strength would be evaluated, but this is usually not possible in patients with acute fracture. A thorough neurovascular assessment of the upper extremity should be performed, with a specific focus on the axillary nerve.

Diagnostic workup should include standard trauma series shoulder radiographs, with the specific focus on an axillary view to ensure the humeral head is not dislocated. Internal and external rotation anteroposterior (AP) views may be useful to assess for tuberosity displacement (Figure 31-1). These radiographs should also be assessed for cortical bone quality. Computed tomography (CT) scan can provide information in assessing fracture morphology. It is useful for identifying dislocation in patients unable to tolerate axillary radiograph and also best identifies head-split morphology. CT scan is also useful for identifying location and comminution of the tuberosity fragments. Finally, a CT scan provides information regarding the status of the humeral shaft and calcar, with extensive bony injury or bone loss in this location potentially identifying the need for cemented humeral prosthesis fixation. A close analysis of fracture lines allows the surgeon to exploit nondisplaced fractures intraoperatively rather than relying on osteotomy creation. There should be a low threshold to obtain CT angiography if radiographs suggest that the humeral head is dislocated medially onto the plexus or there are any abnormal findings present in the neurovascular examination. A vascular surgeon should be available in these cases due to arterial injury risk. Despite the additional information provided by CT scan, an appropriate treatment decision can often be made with an adequately positioned full radiograph series.








SURGICAL TECHNIQUE


Pearls and Pitfalls

In addition to appropriate patient selection, proper surgical technique is imperative for satisfactory outcomes. Hemiarthroplasty is one of the most technically demanding procedures in the realm of shoulder surgery. Specific intraoperative details with a small margin for error will have a tremendous impact on the postoperative function and range of motion. The surgeon must understand the anatomical and biomechanical relationships between the bony, musculotendinous, neurovascular structures of the shoulder girdle. Clinical results are directly correlated with the quality of the reduction and implant positioning. In 2002, Boileau et al15 retrospectively reviewed clinical and radiographic outcomes of hemiarthroplasty for three-part and four-part fractures. Three main, often mutually dependent, factors were identified as being paramount for success: prosthesis position, tuberosity position, and stable fixation. The authors described the “unhappy triad,” excessive retroversion, excessive height, and greater tuberosity distalization, as leading to the worst outcomes. Because of the interdependence of these three factors, authors have recommended against imprecise, or “eyeballing,” methods of prosthesis placement.


Prosthesis Height

Prosthesis height determines the deltoid and rotator cuff tension and ultimate position of the greater tuberosity fragment. Placing the prosthesis too proud lengthens the humerus and puts excessive tension on the rotator cuff. Increasing the length by 10 mm can lead to proximal migration of the prosthesis, displacement of the greater tuberosity, possible superior impingement, and ultimately poor active forward elevation (FE) and pain.16 Placing the prosthesis too proud may also lead to either gapping between the tuberosity fragment and the shaft or the subsequent overreduction of the greater tuberosity and abnormal rotator cuff tension in order to obtain bony apposition with the shaft. There are several methods to ensure the humeral stem is placed at the proper height. One method is to use intraoperative anatomic landmarks. If the medial calcar is intact, the flare of the prosthesis may be placed directly above this just as in standard reconstructive surgery for osteoarthritis. Another useful anatomic landmark is the distance between the superior border of the pectoralis major tendon and the top of the humeral head, which has been measured between 5 and 6 cm in anatomic studies.17 In the fracture setting, however, these anatomic landmarks may be distorted by soft tissue stripping or bony comminution. Prosthesis height may also be determined by templating off of the contralateral humerus. This is done by obtaining preoperative contralateral radiographs that have a radiographic marker for size calibration. Length is measured from the superior apex of the articular surface of the humeral head to
a fixed point distally that can be easily identified intraoperatively (Figure 31-2). The distance is then measured from the distal point proximally to the superiormost edge of the lateral shaft and again to the superiormost edge of the medial shaft. These are each subtracted from the length of the contralateral humerus to find the length of the prosthesis that will be proud on the lateral and medial sides, respectively. These measurements can be marked on the trial and final prosthesis to aid in accurate placement.18 A third method for judging height is what has been called the “jigsaw puzzle method” (Figure 31-3). This method requires reassembling the fracture fragments on the calcar and selecting an anatomic head replacement based on comparison of the complete reconstructed native humeral head or the diameter of the native head. The smaller measured diameter of the head should be used, as the native humeral head is not perfectly spherical. Using the fracture fragments to assemble the proximal humeral anatomy can also help with assessing the fit of the native head on the calcar, which can then be recreated with the prosthesis. Although this method may not be possible in the setting of severe comminution, it is a useful quality check to prevent clinically important height errors.